Cross-built project depending on project with larger set of crossScalaVersions fails to compile

steps

1. Create a new project:

mkdir -p test/project
cd test
echo sbt.version=1.0.0 > project/build.properties

cat > build.sbt <<EOF
lazy val top = project
  .settings(scalaVersion := "2.12.3", crossScalaVersions := Seq("2.11.11", "2.12.3"))
lazy val bottom = (project dependsOn top)
  .settings(scalaVersion := "2.11.11", crossScalaVersions := Seq("2.11.11"))
EOF

1. Run sbt +compile

problem

Compilation fails with:

[error] sbt.librarymanagement.ResolveException: unresolved dependency: top#top_2.11;0.1-SNAPSHOT: not found

expectation

+compile is successful.

notes

sbt version: 1.0.0

Works with sbt-doge. Change sbt.version=0.13.16, add addSbtPlugin("com.eed3si9n" % "sbt-doge" % "0.1.5") to project/plugins.sbt and run sbt 'so compile'.

[jroper]

One work around to this would be to set crossScalaVersions on the root project to contain a single Scala version that all your aggregated projects have in their cross scala versions. If there is a single common Scala version, this will work. Given the existing bug in sbt-doge where the root project was never actually issued any cross built commands, you should be able to set crossScalaVersions to whatever you like on the root project and it won’t have any impact on it.

If that doesn’t work, then you may want to consider using sbt-cross. sbt’s built in cross building support is a hack, fullstop, and there are many scenarios where it won’t work, for example, if you have a sub project A that cross builds against 2.11 and 2.12, and a second sub project B that only builds against 2.11 that depends on A, and a third sub project C that only builds against 2.12 and also depends on A, this setup cannot work - you won’t be able to issue a regular compile on it, and you won’t be able to import it into an IDE. If you’re coming across the problem in this issue, then you’re likely very close to also coming across that issue. In contrast, sbt-cross isn’t a hack (or rather is much less hacky), it’s built to work with the sbt scoping system, it doesn’t hack at it like sbt’s built in cross building uses (though I’m not sure how well IDEs go at importing it because it does mean that the same source folders end up being shared by multiple projects).

[eed3si9n]

A variant of James’s workaround, I think is to set the crossScalaVersions to List(). The root project that sbt injects should probably do that by default.

For all others who are encountering this issue, the workaround would look like:

lazy val root = (project in file("."))
  .aggregate(sharedLib, legacyApp, modernApp)
  .settings(crossScalaVersions := List()) // add this line